My daughter stored her (brand new!) low whistle in a plastic case after playing it. It sat for several months with no use, and when she took it out the wood in the mouthpiece was covered in fungus, and had swollen enough to open the seam in the whistle itself. Can this be repaired? Any thoughts? She lives near New York City. Thank you!
Is there a wooden fipple? What’s the fungus growing on?
Fungi are really nice when baked in salted butter with a fresh pasta to go with them 
Seriously, if it’s a wooden whistle, be aware that some fungi are poisonois… I woudn’t want to put something like that in my mouth. That’s why none of my whistles are stored in airtight places…
It would be very helpful to know which model of whistle this is.
Dilute bleach will kill off any fungus you are likely to have. Only problem, if it is a wooden whistle, you might bleach out the wood if you aren’t careful. If it is metal, just let her rip. There may be safer methods to kill the fungus on a wood whistle. It would be nice to hear of some.
Yeah, bleach is probably the best way to go even with the possible sideeffect of bleaching the wood. Bleach will not only kill off the fungii but will also destroy any of the organic poisons they might have created.
I would rather have a whistle that’s bleached and safe than one that’s looking good and full of carcinogenic poisons… 
Sure it can be repaired. What is the rest of the whistle made of? If only the plug is wood should be able to replace it. The seam that opened can be closed back, unless it is wood also?
In many cases vinegar will kill mold and probably fungus.
Unless they have changed the rules again, fungus and mold are pretty much the same critters.
That’s more or less right. Mold is a fungus, but there are fungi that aren’t molds. My experience is with the molds.
FYI: Killing mold does not render it harmless. Even when dead, toxic mold remains toxic, for example. Many molds can cause severe allergic reactions, particularly when inhaled, and this is true even after the mold has been “killed” with bleach treatment. I know this first hand having had a very bad experience with a moldy flute.
Also, keep in mind that while you may kill mold on the surface of the wood, the mold will have grown down into the wood, chances are you won’t be able to kill it all.
My advice: Move on and get a new whistle. It may be an expensive lesson to learn, but a few hundred bucks isn’t worth the potential health risk.
Loren
I can only second Loren’s advice, moldy wind instrument can be really serious, seen it here with a gaita (was given as a present as it was not played for long). It had mold inside the bag (unknowingly) and from just playing a very short time to try it out Colin came down with a hefty lung infection.
If it is a metal tube with wooden plug, the wood at least should be taken out for sure, metal can be cleaned very well normally from this sort of life forms, but the wood I would not use anymore. On the other hand if you cannot remove the wood without distroying it anyways then just get rid of it and safe the time.
Brigitte
I guess there’s a cautionary tale here for new players who are attracted to the look and feel of a wood whistle, but may be unaware of particular the care and maintenance that woodwinds can require: play-in, oiling, drying, humidity and temperature control, etc.
“Covered in fungus” doesn’t sound very promising. Perhaps the entire head joint can be replaced, if the whistle body is fungus-free. I agree with azw that knowing the whistle in question would help for recommending options.
After a lifetime dealing with persnickety woodwinds, I’m happy to play metal and plastic whistles that are essentially “grab and go”. 